Rub and buzz is a particular type of sound distortion which originates in mechanical faults in loudspeakers (as used herein, speaker and loudspeaker may be used interchangeably). Also referred to as “triggered distortion” in the literature, rub and buzz is an impulsive and unwanted form of non-linear distortion, which is both annoying to the listener and may even damage the loudspeaker. Furthermore, rub and buzz is problematic because it is not easily measurable using normal techniques such as total harmonic distortion (THD) analysis or root-mean-square (RMS) fast Fourier transform (FFT) testing, and therefore often requires human intervention to detect. Rub and buzz distortion is typically caused by mechanical or structural defects in speakers, for example, a misaligned voice coil that rubs due to a bent surround or a loose spider.
FIG. 1 is a diagram of a typical prior art audio output system that includes digital processing module 102, which can have digital filters, digital equalizers and other digital circuitry used to process audio signals. FIG. 1 further includes digital to analog converter (DAC) 104, analog output stages 106 which typically comprise an amplifier and output driver which drives speaker 108. However, no circuitry is available to address the problem of rub and buzz sound distortion.